Revert "Shorten ternary operator"

This reverts commit dfb7d6f.

Author: royklutman

reference/forms/twig_reference.rst

@@ -340,7 +340,7 @@ done by using a public ``vars`` property on the
 .. code-block:: html+twig
 
     <label for="{{ form.name.vars.id }}"
-        class="{{ form.name.vars.required ? 'required' }}">
+        class="{{ form.name.vars.required ? 'required' : '' }}">
         {{ form.name.vars.label }}
     </label>